Loud speaker



April 19, 1932. Q FARRAND 1,855,168

LOUD SPEAKER Original Filed April 22. 1926 2 Sheets-Sheet l INVEEOR WAMy@ 42mg ATTORNEYS April 19, 1932. C, L FARRAND 1,855,168

LOUD S PEAKER Original Filed April 22. 1926 2 Sheets-Sheet 2 PatentedApr. 19, 1932 UNlTEi) STATES PATENT ori-lcs CLAIR L. FARBAND, OF FORESTHILLS, NEW YORK, ASSIGNOR T0 LEKTOPHON'E COR- P OBATION, 0F JERSEY CITY,NEW JERSEY, A CORPORATION 0F DELAWARE LOUD SPEAKER.l

' Original application illed April 22, 1926, Serial No. 103,844. Dividedand this application iiled October 17,

1929. Serial This application is a division of my copending applicationSerial No. 103,844 filed April 22, 1926.

i The invention relates to apparatusfor interconverting electricalenergy and sound Waves such as loudspeakers and so-called pick-ups. Thedevice to be herein disclosed may be used interchangeably as aloudspeaker or as a pick-up and for convenience it will hereinafter bereferred to only by the name loudspeaker.

The invention relates particularly to directacting loudspeakers of thecone type whose actuating motor has an armature connected with the apexportion of the cone and which is movable in a path parallel with thepole faces of the fieldmagnet. The so-called dynamic speaker is of thistype. The motor armature of a dynamic speaker is a coil coaxiallyconnected with the cone and which moves axiallyin an annular air gap.The cone of a dynamic loudspeaker should be supported so that it hassmall elastic restoring force and so that it is capable of a largeamplitude of movement at low frequencies. It has been 'found that whenthe cone is so supported and when there is no other means of support forthe armature coil except the cone itself any displacement of the cone(other than the vibratory displacement in a true axial direction) alsodisplaces the coil, either tilting it or moving it laterally in its airgap so that it is likely to strike the pole faces and interfere with theoperation of the device.

'The principal object of this invention is to provide a loudspeaker ofthe above described general type in which the flexible support for thediaphragm is supplemented by a special flexible support for thearmature, which will permit the armature to move freely in an axialdirection but will hold the armature, or assist the flexible support forthe cone in holding it, in the proper aligned position in the air gap.

Another object of the invention is to provide an improved suspensionsystem for the cone-armature unit of that type of speaker in which acone and armature vibrate axially as a unit, the suspension being suchthat the armature as well as the cone will be guided in al true axialdirection and will be held against lateral tilting or displacement suchas might cause the armature to strike the pole faces of the fieldmagnet.

One form of the invention is illustrated in the accompanying drawings,in which Fig. 1 is a vertical section of a loudspeaker constructed inaccordance with the invention;

Fig. 2 is a vertical section taken on the line 2-2 of Fig. 1;

Fig. 3 is a front elevation of the diaphragm; and

Fig. 4 is a fragmentary sectional view showing a modification of one ofthe details of construction.

The loudspeaker illustrated in the drawings comprises a base 1 whichsupports an annular ring 2. Radial arms 3 extend inwardly from the ring2 and support a cupshaped magnetic field member 4. A central core 5 issecured to and projects from the bottom 6 of the cup-shaped member 4.The

other end of the cup-shaped member 4 is i provided with a circular polepiece 7 which extends radially inward toward the core 5 but only asuflicient distance to form with the end of the core an annular air gapwithin which' a coil 8 may operate. The cup-shaped member 4, the core 5,and the circular pole piece 7 are made of cast iron or other'suitablemagnetizable material. A coil 9 surrounds the core 5 and when energizedproduces a strong magnetic field across the annular air gap in which thecoil 8 operates. The leads 10 and 11 from coil 9 pass rearwardly throughsuitable openings in the bottom of the cup-shaped member 4 and areattached to binding posts 12 and 13 carried by an in sulating support14. The coil 8 is mounted on a cylindrical support. 15 of insulatingmaterial carried by or associated with a spider 16. The leads from thecoil 8 extend through a central opening in the core 5 and are connectedwith binding posts 18 carried by the insulating support 14. The parts s0far described constitute a driving motor of the so-calledelectro-dynamic type. The cone to which the armature coil 8 is connectedis shown at 19. So farl as the flexible support for the coil (to behereinafter described) is concerned the cone may be supported in anysuitable manner which will give it small elastic reaction and whichwill'permit it to have a large amplitude of movement at low frequencies.In the form of the device shown in the drawings the cone is supported asfollows: The apex of the cone is connected to a rod 17 by means" of thenuts 20. The armature coil 8 is also connected to this rod by means ofthe spider 16. The outer end of the rod 17 is connected to the edgeportion of the cone by a number of radial cords or wires 26, in orderthat the periphery of the cone will be held in a fixed position relativeto the rod 17. The cords or wires 26 may be attached in any suitable wayto the cone as by means of buttons or the like 27. The cords or wires 26move bodily with the rod 17 and the cone 19 and in no way constrain theaxial movement of the cone. The outer end of the rod 17 is alsoconnected by means of radially extending wires or cords 25 to aplurality of rods 22 which connect the annular ring 2 to a spacedannular ring 23. The annular rings 2 and 2 3 together with theconnecting rods 22 constitute a skeleton framework inside of which thecone and the armature coil are suspended. The cords `or wires 25constitute a flexible support for the cone located substantially in theplane of its base and which permits the cone to move freely in an axialdirection with very small elastic reaction. The resilient support forthe armature coil, in the form of the device shown in the drawings, issubstantially like the resilient support for the cone. It comprises anumber of radially extending wires or cords 24 connected at their innerends to the rod 17 near the coil 8 and at their outer ends to the rods22. This fiexible support prevents lateral displacement of the co1l 8,permits free axial movement of it, imposes a minimum amount of elasticreaction on the coil and perhaps with some aid from the set of cords 25guides the coil 8 in a true axial direction in a path parallel with thepole faces of the field magnet without tilting or lateral movement suchas would cause it to strike the polefaces.

In Figures 1 and 2 the wires or cords 24 and 25 are shown connectedtothe rods 22 through the intermediary of spring members 28 each ofwhich may be adjusted by means of an adjusting screw 29. By regulatingthe screws 29 the position of the rod 17 and the coil 8 may be adjustedradially so that the coil will occupy the proper position in the air.gap and so that the axis of the cone will be in proper alignment withthe axis of the motor. If desired the wires or cords 24 and 25 may beconnected directly to the rods 22 as shown in Figure 4. It may bedesirable to provide at least one of the cords 24 and at least one ofthe cords 25 with a resilient portion 30 in order to produce a slighttension on all of the cords. The resilient portion 30 may be made ofrubber or other suitable material.

The cone 19 is preferably made of fibrous material such as paper and isof shallow conical form. It is of sufficient size to directly reproducethe sounds without the use of a sound box or horn. In other words, it isa direct-'acting diaphragm. The edge of the cone may be bent back'asshown at 21 to provide a circular reinforcement which assists inmaintaining the circular shape of the edge of the cone.

If the device is used as a loudspeaker the coil 9 is energized from anysuitablesource of direct current by connecting conductors to the bindingposts 12 and 13. This will produce a strong magnetic field across theair gap in which the coil 8 operates. The coil 8 is connected in theoutput circuit of a radio receiving set or the like through the bindinlgpost 18. The variations in current throng the coil 8 will cause it tovibrate in a well known manner and these vibrations are transmittedthrough the rod 17 to the cone 19. If the device is used as a pick-upthe coil 9 is energized as before but the coil 8 is connected throughthe binding posts 18 to the input circuit of any system 1n which it isdesired to utilize the current enerated by the movement of the coil 8.ound waves which impinge upon the cone 19 cause it to vibrate and thesevibrations are transmitted to the coil 8. The coil 8 moving in themagnetic fieldV will generate a current which varies in accordance withthe vibrations of the cone 19 in the well known manner.

Inasmuch as the important feature of the invention is the resilientsupport for the motor armature, the resilient support for the cone matake other forms than that herein disclose but it should preferably besubstantially at the plane of the base Iof the cone and should permitthe cone to vibrate freely in an axial direction with small elasticreaction and with a large am litude of movement at low frequencies. fcourse, such a support at or near the-base of the cone assists somewhatthe flexible support for the coil in bringing about the resultshereinbefore described, but it is obvious that without the specialflexible support for the coil, the cone support would not of itselfmaintain the coil in its proper position in the air gap.

Likewise, the resilient support for the coil -may take other forms thanthat herein disclosed. It may be considered as a flexible support, otherthan or supplementary to, the flexible support located at or in thevicinity of the plane of the base of the cone and comprising at leastthree radially extending flexible members connected at .one portion tothe armature structure close to the armature and 'at another portion toa rigid part of the the unit made up of the cone 19 and the armarmaturewhile and parallel l magnet structure faces form an air gap 1n aturecoil 8 which serves to flexibly support the unit (and thereby thearmature) in such a way that the unit is held against lateraldisplacement or tilting movements such as might cause the armature tostrike the pole faces of the field magnet.

I claim:

1. A loudspeaker comprising a direct-acting cone, supporting means forthe cone located substantially at the plane of the base of the cone andhaving flexibility to permit axial vvibration of the cone, an actuatingmotor having a field magnet structure provided with pole pieces havingopposing faces which form an air gap, an armature connected with theapex portion of the cone and movable b etween the pole faces within theair gap and f in a rectilinear path4 parallel with the pole faces, andsupporting means for said armature in addition to said supporting meansfor the cone, said armature supporting means having flexibility topermit vibration of the armature in its path parallel with the polefaces but adapted to hold the armature against displacement in alldirections at right angles to said path.

2. The combination of a Adirect-acting cone which is free tovibrateaxially with negli 'ble elastic reaction, an armature connectwith theapex portion of said cone, a eld having' pole pieces whose which saidarmature moves in a path parallel with said faces and parallel with theaxis of the cone, and a flexile support for armature located adjacent toitand permitting free axial vibration of the preventing itsvdisplacement in all radial direction.v

3. The combination of a direct-acting cone which is free to vibrateaxially with negligible elastic reaction, an armature connected with theapex portion of said cone, a field magnet structure having pole pieceswhose faces form an air gap in which said armature moves in a pathparallel with said faces with theaxis ofthe cone, and a flexible supportfor the nit formed by the cone and armature comprising a plurality offlexible members rigidly supported at one tor having a field magnetstructure provided with pole pieces whose faces form an air gap, anarmature connected with the apex portion of the cone and movable in apath parallel with the faces of said poles, and supporting means foi`said armature in addition to said supporting means for the cone, saidarmature supporting means comprising at least three radially extendingflexible members rigidlysupported at one portion and connected atanother portion to the armature structure near the armature.

5. A loudspeaker comprising a direct-acting cone, a flexible support forthe cone permitting it to vibrate axially, an actuating motor comprisinga field magnet structure having pole faces forming an annular air gapand an annular armature connected with the apex portion of the cone andreciprocable axially in said gap between said pole faces, and a supportfor the armature having flexibility to permit vibration of the armaturein the direction of its axis but adapted to hold the armature againstdisplacement in all radial directions.

In testimony whereof I affix my signature.

CLAIR L. FARRAND.

portion and connected at another portion to said unit adjacent to thearmature, said members preventing movement of the armature in all radialdirections while permitting free axial vibration thereof.

4. A loudspeaker comprising a direct-acting cone, supporting means forthe cone l0- cated substantially at the plane of the base of the coneand having flexibility to permit axial vibration of the cone, anactuating mo-

